In a wireless communication system, there may be multi-RAT user equipment (UE) with capability for access to two or more radio access technologies (RATs). In order to access specific RAT, connection is established to specific RAT and data is transmitted and received based on UE request. However, even if the multi-RAT UE has capability of accessing two or more RATs, the multi-RAT UE cannot simultaneously access multiple RATs. That is, currently, even if a UE has multi-RAT capability, the UE cannot simultaneously transmit and receive data through different RATs.
Since it is not necessary for a legacy multi-RAT technology to have interworking between a wireless LAN and a cellular network, there is a problem in that overall system efficiency is low. Moreover, although a UE has capability of accessing multiple RATs at the same time, it is able to access multiple RATs at the same time in a manner of supporting flow mobility/IP-flow mapping in a network level only without a control in a radio level. For this reason, a legacy technology does not request any control connection between an AP and a cellular network and has been in progress based on a request of a user equipment.
Yet, since the legacy technology is unable to identify a precise situation of a network and selects a UE-oriented RAT, there exists a limit for enhancing overall network efficiency. In particular, since a UE is capable of accessing a plurality of communication systems, it is necessary to have methods for performing data switching from a specific communication system to a different communication system. However, a study on the methods has not been performed yet.